5.1.1

Chapter 22 Motion tracking 976
In this example, a mask is tracked to a moving car so the car can be isolated from the rest of the
clip. The illustration on the left shows the original unmodied clip. In the illustration on the right,
the tracked mask isolates the car (and can be seen as the desaturated background), allowing
separate eects to be applied to the car and its background even though they are part of the
same image. The mask protects the car from the eects of the heavy blur and desaturation.
As with all behaviors, you can drag or copy (Option-drag) a Track Points behavior to a new shape
in the Layers list. When you apply the behavior to a new shape, the trackers are applied to the
control points of the new shape. If the new shape has more control points than the originally
tracked shape, only the original track points are applied. For example, if the originally tracked
shape has three control points, and the new shape has ve control points, trackers are applied
to the rst three control points of the new shape. If the new shape has fewer control points than
the originally tracked shape, trackers are applied to the existing points on the new shape.
Note: Paint strokes usually have a large number of control points. Simplify a paint stroke by
deleting or disabling control points before applying a Track Points behavior to the stroke. To track
the stroke as a whole, rather than by its control points, use the Match Move behavior.
Apply the animation of one shape to the control points of another shape
Applying the animation of one animated shape to another is an easy way to create fun,
complementary animations in which the objects appear to play with each other. For this
workow, your project must contain an object animated with keyframes or behaviors.
1 In a project that contains two shapes, animate one of the shapes using keyframes or a Basic
Motion behavior.
In this example, a simple line shape is animated with the Spin behavior.
For more information about animating with keyframes, see Keyframing overview on page 439.
For more information about Basic Motion behaviors, such as the Spin behavior see Spin on
page 328.
2 Apply the Track Points behavior to a nonanimated shape.
The Track Points behavior inherits the animation data of the animated object closest to it in the
Layers list. (A thumbnail of the animated object appears in the Source well of the Track Points
Behaviors Inspector.)
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